The present invention relates to a device for varying the effective length of the intake pasage of an internal combustion engine.
It has been known that the charge efficiency of an internal combustion engine can be improved by controlling the length of the intake air passage in accordance with the engine speed. More specifically, it is known that a better charge efficiency can be achieved by using a longer intake passage length for lower engine speeds and a shorter intake passage length for higher engine speeds.
An example of a device which takes advantage of this principle is disclosed in Japanese Laid-Open Patent Application No. 50-20126. Therein is disclosed an intake passage length varying device in which two intake pipes are mounted coaxially, one of which is fixed and the other of which is slidable linearly with respect to the other. Although indeed capable of varying the intake passage length, this device is disadvantageous in that it requires a complicated drive and control mechanism and cannot be made compact, requiring a great deal of space for mounting.